The crustacean sinus gland provides a discrete cluster of peptidergic secretory axon terminals, amenable to direct and comprehensive analysis of peptide content by High Performance Liquid Chromatography (HPLC). Previous studies have demonstrated the preponderance of growth regulating (molt inhibitory) and biosynthetically associated peptides in the axon terminals of the sinus gland. Further, differences in peptide content have also been observed across species, suggesting variation in cleavage sites of common prohormone(s) across species. Specifically, it is proposed to determine the amino acid compositions of peptides isolated by HPLC from sinus glands of a number of crustacean species. Comparison with amino acid compositions of peptides already sequenced and/or being sequenced in land crab and american lobster will suggest the occurrence or absence of certain cleavages. A well chosen data set will yield insight as to the evolutionary rate of utilization of novel cleavage sites. Precise studies of rates of utilization of novel proteolytic cleavage sites for a given prohormone are, to my knowledge, not available. However, it is important to gain some insight here: Evolutionary rapid variations in utilized cleavage sites will rapidly change the peptide mixture released by peptidergic neurons. Many prohormones are thought to coordinate complex biological processes through the release of synergistically acting peptide sets: Rapid variation in utilized cleavage sites may provide a mechanism for rapid evolution of complex physiological or behavioral responses.